Here's a pacu:
Often the smaller ones will be silver instead of slate gray, very much like a "silver dollar fish" that you can buy at the pet store. They still really don't look much like pompano though.
Also note that they are in the pirhana family, and they have teeth:
The teeth are not as sharp as a pirhana's but they are often capable of biting through light line.
All in all, I think it's a real long shot that it's an aquarium fish. I mean it's possible, but just awfully unlikely. I think it's more likely that we've got a regular native species that was either not looked at very clearly, or maybe even a little deformed or something, and now hard to identify without a photo. That's usually the case.
bd
